The biobehavioral model for the CEBASM expands the work of the P20 Center on interactions among biological and behavioral phenomena by focusing on the advancement of biobehavioral clinical science through research related to biobehavioral mechanisms, management, and outcomes of complex constellations of symptoms, including the commonly occurring symptom of fatigue. Biobehavioral research focuses on the interactions among biological, behavioral, and social factors and their effects on outcomes\ The general model depicted in Figure 2 has been used by the individual Project Directors as a foundational framework for examining fatigue and associated biobehavioral phenomena specific to their pi^oposed projects. Specific aims of Center Projects include investigation of biobehavioral science specific to understanding and managing fatigue and associated symptom constellations and their impacts on biobehavioral health outcomes across diverse populations. Serving as the guiding conceptual framework for the CEBASM, the expanded model represents the interaction of biological and behavioral variables as well as critical cofactors in the context of a crifical health experience. A critical health experience involves a dramatic change in health or a perception of change in relation to health that places an individual at risk. The symptom experience unfolds as psychosocial and behavioral moderators (including biobehavioral symptom management interventions) interact with biological mediators. In the biological domain Center research focuses on the multidimensional interactions among neuroendocrine and immunological mediators that may underiie symptom constellafions. These complex interactions in the context of a crifical health experience are thought to explain, at least in part, commonly occurring symptoms such as fatigue and psychological distress and, ultimately, biobehavioral outcomes in the domains of psychosocial functioning, quality of life, and physical health. Additionally, numerous moderators, including person factors, known and unknown confounding variables, as well as indirect covariates, contribute to symptom experiences and biobehavioral health outcomes.